The lovely, tennis-style dress by Catherine Walker with poppy print towards the hemline was teamed with the same Victoria Beckham handbag the 35-year-old British royal carried to the opening day.
Kate is the patron of the All England Lawn Tennis and Croquet Club, a role she recently took over from Queen Elizabeth.
Charlotte, two, and three-year-old George were last seen in public on Buckingham Palace's balcony watching the flypast following the Trooping the Colour ceremony. Later this evening the duke and duchess are scheduled to attend a formal dinner at the Royal Łazienki park.
Prince George and Princess Charlotte started their week-long two country tour in Poland. Kate'slittle girl adjusted quickly and was delighted to show off her red-and-white print dress and matching bright red shoes as she snuggled in her mother's arms.
Kensington Palace has said the young prince and princess will be seen on limited occasions over the course of the week.
The royal family will then head to Germany, where the Duke and Duchess of Cambridge will meet with Chancellor Angela Merkel, visit Berlin's Brandenburg Gate, and stroll through a traditional beer garden in Heidelberg.
While William and Kate are tending to royal duties, George and Charlotte will be with their nanny, but hopefully we'll get to catch a few more glimpses of them before the tour ends.
Also in the Baltic port city, Kate and William will visit the European Solidarity Centre museum, which tells the story of the Soviet bloc's only free trade union.
Wimbledon has officially come to an end, the couple will fly this Monday, July 17 for an official five-day trip to Poland and Germany.